Pseudo-plastic behavior of uraniumniobium alloys

ABSTRACT

THE PRESENT INVENTION PROVIDES A PROCESS FOR ACHIEVING AN UNUSUAL, THERMALLY RECOVERABLE AND REVERSIBLE, PSEUDOPLASTIC STRAIN BEHAVIOR IN URANIUM-NIOBIUM ALLOYS, AS WELL AS USEFUL PRODUCTS PREPARED THEREFROM. THE PROCESS COMPRISES RAPIDLY COOLING A URANIUM-NIOBIUM ALLOY FROM THE GAMMA REGION, PLASTICALLY DEFORMING THE SAME AT A TEMPERATURE BELOW 450*C., AND SUBSEQUENTLY HEATING OR COOLING THE ALLOY TO CAUSE IT TO EXHIBIT PSEUDO-PASTIC BEHAVIOR.

March 2, 1971v JACKSON ET AL 3,567,523

PSEUDO-PLASTIC BEHAVIOR OF URANIUM-NIOBIUM ALLOYS Filed Sept. 27, 1968 SCHEMHT/C DRflW/NG /LLU5TR/I7'/N6 THE THERMQLLY RECOVER- HBLE HND PHR T/HLLY REVERSIBLE, PSEUDO-PLHST/C .STRfl/N Bf HfiV/OR. THFSTEPS CORRESPOND 70 THE SEQUENCE OF EVE/V75 DESCRIBED IN THE TEXT Be /a w amb/ern flmbien/(l'o) 05 quenched 5/70 06 Re vers/b/e 460 ye 0m b/en r; (7,) 5/10 e Amb/en/(To) Revers/b/e berm sh ape INVENTORS R0 as J. Jack son Joseph 5 50/0/70 Ju/ius L. Frankeny magw United States Patent 3,567,523 PSEUDO-PLASTIC BEHAVIOR OF URANIUM- NIOBIUM ALLOYS Ross J. Jackson, Boulder, Joseph F. Boland, Golden, and Julius L. Frankeny, Arvada, Colo., assignors to The Dow Chemical Company, Midland, Mich.

Filed Sept. 27, 1968, Ser. No. 763,180 Int. Cl. C22c 27/00; C22f 1/18 US. Cl. 148--11.5 Claims ABSTRACT OF THE DISCLOSURE The present invention provides a process for achieving an unusual, thermally recoverable and reversible, pseudopla-stic strain behavior in uranium-niobium alloys, as well as useful products prepared therefrom. The process comprises rapidly cooling a uranium-niobium alloy from the gamma region, plastically deforming the same at a temperature below 450 C., and subsequently heating or cooling the alloy to cause it to exhibit pseudo-plastic behavior.

BACKGROUND OF THE INVENTION The invention described herein was made in the course of, or under, a contract with the United States Atomic Energy Commission.

This invention relates to a process for achieving an unusual, thermally recoverable and reversible, pseudo-plastic strain behavior in certain uranium-niobium alloys and to useful products prepared therefrom.

While the alloy compositions used in the present inven tion are known, the process of the present inventon, unexpectedly, results in the achievement of new and nonobvious products from said alloys. The application of the present process to uranium-niobium alloys results in the achievement of pseudo-plastic behavior in said alloys, wherein substantially complete reversibility is achieved at temperatures both above and below the initial deformation temperature. The process of the present invention, consequently, makes said alloys useful in numerous ways. For example, the alloys treated as described herein behave similarly to bimetallic strips and could act in their place. Such alloys are useful in satellites as heat controlled folding or unfolding devices. They are also useful as lock washers and lock nuts.

OBJECTS OF THE INVENTION It is a principal object of the present invention to provide a novel process for achieving pseudo-plastic behavior in uranium-niobium alloys.

It is another object of the present invention to provide novel uranium-niobium alloy products which exhibit pseudo-plastic behavior.

These and other objects and advantages of the present invention readily will become apparent from the detailed description presented hereinafter.

A schematic diagram of process steps of the present invention is shown in the accompanying drawing.

SUMMARY OF THE INVENTION In one embodiment, the present invention is a process for achieving an unusual, thermally recoverable and reversible, pseudo-plastic strain behavior in uranium-niobium alloys wherein the niobium atom percent is in the range of from a minimum of about 5 to a maximum of about 23. The invention further comprehends useful products prepared from the processed alloys. The process of the present invention comprises (1) rapidly cooling (e.g., within about 10 seconds) a uranium-niobium alloy from a temperature at which the particular alloy exhibits a gamma structure (e.g., from about 640 C. to about the solidus temperature), (2) plastically deforming (e.g. bending) said alloy at a temperature, herein designated T below about 450 C. shaped articles are formed from the alloy prepared in this manner and deformed along a major axis. If after initial deformation at T the alloy is cooled to some temperature, T below T the sample deforms slightly in the direction of the original bend; upon subsequent heating to T the sample unbends in the direction of the undeformed shape. This process is reversible between T and T An additional embodiment of the process of the present invention comprises, after steps (1) and (2) as hereinbefore described, heating the alloy to a temperature, T above T to cause reversion of the alloy shape to that of the undeformed alloy. On subsequent and continued temperature cycling, the alloy unbends and rebends in a near reversible manner as long as temperature T is not exceeded.

PREFERRED EMBODIMENTS OF THE INVENTION In accordance with a preferred embodiment of the present invention, a sample of a uranium-niobium alloy material, wherein the niobium atom percent is in a range of from a minimum of about 5 to a maximum of about 23, is cooled rapidly, preferably water quenched from the 7 region. Prior to bending the alloy sample, surface film is removed from the sample, ordinarily by means of electro-polishing. The sample is bent, at a temperature, to T below about 450 C., a predetermined distance by any suitable bending mechanism such as, for example, a bending jig. The lower the temperature at which the bend is made, the more pronounced and more reversible is the ultimate pseudo-plastic behavior of the alloy. Preferably the initial bend temperature is below C.

If subseqeunt to the initial bend, the sample is cooled to a lower temperature, T the sample bends slightly in the direction of the initial deformation. On warming said cooled sample to temperature T the sample reverts back to the initial degree to deformation. This bending-unbending process between T and T is reversible.

If said alloy is, subsequent to the initial deformation at T heated to higher temperature T the sample unbends in the direction of its undeformed shape. On cooling to T said sample rebends but only recovers about /2 the amount unbent in the previous step. On subsequent and continued temperature cycling, however, said sample unbends in a near reversible manner as long as the upper temperature does not exceed T Although some reversibility is exhibited at higher temperatures, for nearly complete reversibility the upper temperature, T should not exceed about 275 C.

Preferably, the heating and cooling of the deformed alloy sample is conducted in an isothermal manner. For example, a dilatometer and sample are placed in a first bath at T and held there until unbending ceases; the dilatometer and sample are then transferred to a second bath at T and held there until bending ceases.

The present invention has been found to be particularly suitable for use with uranium-rich niobium binary alloys wherin the niobium atom percent is from about to about 23%. Preferably uranium-rich niobium alloys having from about 9 to about 18 atoms percent niobium are employed.

A uranium-rich niobium alloy having about atom percent niobium appears to give the maximum dimensional changes with temperature cycling.

A better understanding of the subject matter claimed are set forth to illustrate and are not to be construed to limit the present invention.

EXAMPLE I A flat bar of a uranium-rich niobium alloy material measuring 2.0 x 0.375 X 0.061 inches, was solution quenched from the gamma temperature region, after heat treatment for 4 hours at 850 C. A light weight tantalum quenching fixture was used to assure a flat starting specimen. The alloy bar was then electropolished to remove any oxide surface film. The bar was then bent a predetermined distance at room temperature on a bending jig. The alloy samples were bent until the center of the sample encountered the base of the bending jig. The bent sample was then placed in a simple dilatometer and the amount of thermally induced bending measured as a function of temperature and time.

The heating and cooling of the sample was conducted in an isothermal manner. That is, the dilatometer and sample were placed in one bath at temperature T and held there until unbending ceased. The dilatometer and sample were then transferred to a bath at T and held there until the bending ceased. This procedure was carried out through 6 complete cycles. A silicone oil was used as the heating medium at temperatures from 0 to 290 C. Above 290 C. a vertical mufiie furnace with an argon atmosphere was used. Liquid nitrogen was used for the 196 C. bath. A Dry-Ice trichloroethylene slurry was used for the 70 C. bath.

The process of the present invention was performed on the following alloys: U-12 atom percent Nb, U-lS atom percent Nb, U-18 atom percent Nb, U-9 atom percent Nb, and 304 stainless steel alloy, as a control.

The process of the present invention was performed on U-9 atom percent Nb sample at the following temperature atom percent Nb sample at the following temperature cycles: (T 'cT 0 ,l50 C.; 0:250 C.; 0. 350 C.; on the U-15 atom percent Nb sample and the 304 stain less steel sample at the following temperature cycles; (T ':T 0:196 C.; 0a:70 C.; 0?60 C.; 0. 95 C.; 0:150 C.; 0:205 C.; 0:250 C.; 0:37S C.; on the U-18 atom percent Nb sample at the following temperature cycles: (T ':T 0:196 C.; 0. *150 C.; 0:250 C.; 0. *350 C.

A temperature cycle T :T 1 indicates that the alloy was deformed at an intermediate temperature, T which in the instant case was ambient room temperature. Subsequently, the sample was cooled to T and heated to T as depicted in the drawing.

' The following results were observed: (1) All samples, except the 304 stainles steel, exhibited the unusual, thermally recoverable and reversible, pseudo-plastic behavior. (2) All samples, except the 304 stainless steel, bent in the direction of the original bend on cooling to a lower temperature, T (below initial bend temperature) and on subsequent warming of such samples to T they reverted to their initial deformed shape. This process was found to be reversible. (3) on heating the sample to a temperature T above initial bend temperature, T the sample unbent, often reaching the as-quenched or unbent shape.

a maybe obtained in light'of the following examples which L (4) On subsequent cooling, the sample rebends but only recovers about /2 the amount unbent in step (3). (5) On continued temperature cycling, the sample unbends and rebends in a near reversible manner as long as the upper temperature in step (3) is not exceeded. Also, the upper temperature must be less than about 275 C. for the change to be near reversible. (6) The thermally recoverable and reversible behavior was maximized in the U atom percent Nb alloy.

EXAMPLE 'II The effect of cycling at a lower temperature on subsequent cycling at higher temperatures was tested. A

U'-l5 atom'percent'Nb" sample, treated 'by the process of" this invention, was tested in the following sequence of temperature cycles (T ':T 23:196 C.; 0:90 C.; 0:l65 C.; 0:215 C.; 0:250 C.; 0:350" C.; 0":400 C.

-It was found that the lower temperature cycles do not have a large effect on subsequent cycling at higher temperatures.

EXAMPLE III A U-15 atom percent Nb alloy was bent at room temperature in the normal manner, that is the sample had not previously undergone quenching from the gamma region. The sample was then jigged to maintain the bent shape and heated to 850 C. and subsequently water quenched. The sample was then subjected to dilatometric analysis on thermal cycling in the manner of the present invention. No motion of the sample was observed. Thus, plastic deformation of the quenched shape is required to achieve the results of the present invention.

Various modifications can be made in the present invention without departing from the spirit or scope thereof for it is understood that we limit ourselves only as defined in the appended claims.

We claim:

1. A process for achieving thermally recoverable and reversible pseudo-plastic strain behavior in alloys, said alloys being selected from the group consisting of uranium-rich niobium alloys wherein the niobium atom percent is from a minimum of about 5 to a maximum of about 23, which comprises quenching said alloy from the gamma region and plastically deforming the alloy at temperatures below about 450 C.

2. The process of claim 1 wherein thermally recoverable and reversible pseudo-plastic strain behavior is achieved at temperatures above the initial deformation temperature by the additional step of heating the plastically deformed alloy to a temperature above the initial deformation temperature.

3. The process of claim 1 wherein thermally recoverable and reversible psuedo-plastic strain behavior is achieved at temperatures above the initial deformation temperature by the additional step of heating the plastically deformed alloy to a temperature above the initial deformation temperature but below 275 C.

4. The process of claim 1 wherein the alloy is selected from the group consisting of uranium-rich niobium alloys wherein the niobium atom percent is from about 9 to about 18%.

5. The process of claim 1 wherein the alloy is uranium 15 atom percent niobium.

6. A process for achieving thermally recoverable and reversible pseudo-plastic strain behavior in alloys, said alloys being selected from the group consisting of uranium-n'ch niobium alloys wherein the niobium atom percent is from about 5 to about 23, which comprises:

(a) heating said alloy to a temperature of about 850 C.,

(b) quenching said alloy within about 10 seconds, and

(c) plastically deforming the alloy at a temperature below about 450 C.

7. The process of claim 6 wherein the alloy is water quenched to room temperature.

6 8. A process for achieving thermally recoverable and References Cited reversible pseudo-plastic strain behavior in a shaped ar- UNITED STATES 1P ATENTS hole of an alloy selected from the group consisting of uranium rich niobium alloys wherein the niobium atom 2,830,896 4/1958 Seybolt 148'158 percent is from a minimum of about 5 to a maximum of 5 2914433 11/1959 McGearY a1 75 122-7 about 23, which comprises quenching said article from 3,243,350 3/1966 Lustman et a1 75-12] the gamma region of the alloy and plastically deforming the article along a major axis at a temperature below HYLAND BIZOT Pnmary Exammer about 450 C. W. W. STALLARD, Assistant Examiner 9. Alloys exhibiting thermally recoverable and reversi- 10 ble pseudo-plastic strain behavior as produced by the process of claim 1. '75--l22.7

10. Shaped articles as formed by the process of claim 8.

US. Cl. XJR- 

